U.S. patent application number 13/529277 was filed with the patent office on 2012-12-27 for amoled panel and driving circuit and method therefor.
This patent application is currently assigned to CHENGDU BOE OPTOELECTRONICS TECHNOLOGY CO., LTD.. Invention is credited to Xiaojing QI, Wen TAN.
Application Number | 20120327064 13/529277 |
Document ID | / |
Family ID | 46693191 |
Filed Date | 2012-12-27 |
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United States Patent
Application |
20120327064 |
Kind Code |
A1 |
QI; Xiaojing ; et
al. |
December 27, 2012 |
AMOLED PANEL AND DRIVING CIRCUIT AND METHOD THEREFOR
Abstract
Embodiments of the present disclosure relates to an active
matrix organic light emitting diode (AMOLED) panel and the driving
circuit and method therefor. The driving circuit of the AMOLED
panel comprises: a driving transistor; a first transistor; a second
capacitor; an organic light emitting diode; a voltage adjustment
module, which is connected to a first control signal terminal, a
second control signal terminal and a high level signal terminal,
and is connected with the second capacitor, the driving transistor
and the first transistor, for adjusting a gate-source voltage of
the driving transistor connected with the second capacitor, such
that a driving current of the driving transistor in a saturation
status is independent of its threshold voltage.
Inventors: |
QI; Xiaojing; (Beijing,
CN) ; TAN; Wen; (Beijing, CN) |
Assignee: |
CHENGDU BOE OPTOELECTRONICS
TECHNOLOGY CO., LTD.
Chengdu
CN
BOE TECHNOLOGY GROUP CO., LTD.
Beijing
CN
|
Family ID: |
46693191 |
Appl. No.: |
13/529277 |
Filed: |
June 21, 2012 |
Current U.S.
Class: |
345/212 ;
345/82 |
Current CPC
Class: |
G09G 3/32 20130101; G09G
2300/0819 20130101; G09G 2300/0861 20130101; G09G 2300/0852
20130101; G09G 3/3233 20130101; G09G 2320/045 20130101 |
Class at
Publication: |
345/212 ;
345/82 |
International
Class: |
G09G 3/32 20060101
G09G003/32; G06F 3/038 20060101 G06F003/038 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 21, 2011 |
CN |
201110168038.6 |
Claims
1. A driving circuit of an active matrix organic light emitting
diode (AMOLED) panel, comprising a driving transistor, a first
transistor, a second capacitor, an organic light emitting diode,
and a voltage adjustment module, wherein the driving transistor
comprises a gate which is connected to the second capacitor, a
source which is connected to a low level signal terminal, and a
drain which is connected to the voltage adjustment module; the
first transistor comprises a gate which is connected to a row scan
signal terminal, a source which is connected to the voltage
adjustment module, and a drain which is connected to a data signal
terminal; the second capacitor is connected between the gate of the
driving transistor and the low level signal terminal; the organic
light emitting diode is connected between the low level signal
terminal and a juncture of the source of the driving transistor
with the second capacitor, or is connected between a high level
signal terminal and the drain of the driving transistor; and the
voltage adjustment module is connected to a first control signal
terminal, a second control signal terminal and the high level
signal terminal, and further is connected with the second
capacitor, the gate of the driving transistor, and the source of
the first transistor, for adjusting a gate-source voltage of the
driving transistor connected with the second capacitor, such that a
driving current of the driving transistor in a saturation status is
independent of the threshold voltage of the driving transistor.
2. The driving circuit of an AMOLED panel according to claim 1,
wherein the voltage adjustment module includes: a second
transistor, a gate of which is connected to the first control
signal terminal, a source of which is connected to the second
capacitor, and a drain of which is connected to the drain of the
driving transistor; a third transistor, a gate of which is
connected to the second control signal terminal, a source of which
is connected to the drain of the driving transistor, and a drain of
which is connected to the high level signal terminal; and a first
capacitor, which is connected between the source of the first
transistor and the second capacitor.
3. The driving circuit of an AMOLED panel according to claim 2,
wherein when the organic light emitting diode is connected between
the high level signal terminal and the drain of the driving
transistor, the organic light emitting diode is connected between
the high level signal terminal and the drain of the third
transistor.
4. The driving circuit of an AMOLED panel according to claim 2,
further including a fourth transistor, a gate of which is connected
to the row scan signal terminal, a source of which is connected to
one end of the organic light emitting diode, and a drain of which
is connected to the other end of the organic light emitting
diode.
5. The driving circuit of an AMOLED panel according to claim 3,
further including a fourth transistor, a gate of which is connected
to the row scan signal terminal, a source of which is connected to
one end of the organic light emitting diode, and a drain of which
is connected to the other end of the organic light emitting
diode.
6. The driving circuit of an AMOLED panel according to claim 4,
wherein the driving transistor and the first to fourth transistors
are N-type transistors.
7. The driving circuit of an AMOLED panel according to claim 5,
wherein the driving transistor and the first to fourth transistors
are N-type transistors.
8. An active matrix organic light emitting diode (AMOLED) panel,
comprising a plurality of sub-pixel units arranged in matrix, a
driving circuit according to claim 1 being provided to each of the
sub-pixel units.
9. The AMOLED panel according to claim 8, wherein the driving
circuit comprises a voltage adjustment module including: a second
transistor, a gate of which is connected to the first control
signal terminal, a source of which is connected to the second
capacitor, and a drain of which is connected to the drain of the
driving transistor; a third transistor, a gate of which is
connected to the second control signal terminal, a source of which
is connected to the drain of the driving transistor, and a drain of
which is connected to the high level signal terminal; and a first
capacitor, which is connected between the source of the first
transistor and the second capacitor.
10. The AMOLED panel according to claim 9, wherein when the organic
light emitting diode is connected between the high level signal
terminal and the drain of the driving transistor, the organic light
emitting diode is connected between the high level signal terminal
and the drain of the third transistor.
11. The AMOLED panel according to claim 9, wherein the driving
circuit further includes a fourth transistor, a gate of which is
connected to the row scan signal terminal, a source of which is
connected to one end of the organic light emitting diode, and a
drain of which is connected to the other end of the organic light
emitting diode.
12. The AMOLED panel according to claim 10, wherein the driving
circuit further includes a fourth transistor, a gate of which is
connected to the row scan signal terminal, a source of which is
connected to one end of the organic light emitting diode, and a
drain of which is connected to the other end of the organic light
emitting diode.
13. The AMOLED panel according to claim 11, wherein the driving
transistor and the first to fourth transistors are N-type
transistors.
14. A driving method of an active matrix organic light emitting
diode (AMOLED) panel, comprising: driving the AMOLED panel with the
driving circuit according to the claim 1 for each sub-pixel units
of the AMOLED panel, such that a driving current of the driving
transistor under a saturation status in the driving circuit is
independent of the threshold voltage of the driving transistor.
15. The driving method of an AMOLED panel according to claim 14,
wherein a gate-source voltage of the driving transistor is adjusted
such that the driving current of driving transistor in the
saturation status is independent of its threshold voltage.
16. The driving method of an AMOLED panel according to claim 15,
wherein driving circuit comprises a voltage adjustment module
including: a second transistor, a gate of which is connected to the
first control signal terminal, a source of which is connected to
the second capacitor, and a drain of which is connected to the
drain of the driving transistor; a third transistor, a gate of
which is connected to the second control signal terminal, a source
of which is connected to the drain of the driving transistor, and a
drain of which is connected to the high level signal terminal; and
a first capacitor, which is connected between the source of the
first transistor and the second capacitor.
17. The driving method of an AMOLED panel according to claim 16,
wherein when the organic light emitting diode is connected between
the high level signal terminal and the drain of the driving
transistor, the organic light emitting diode is connected between
the high level signal terminal and the drain of the third
transistor.
18. The driving method of an AMOLED panel according to claim 16,
wherein the driving circuit further includes a fourth transistor, a
gate of which is connected to the row scan signal terminal, a
source of which is connected to one end of the organic light
emitting diode and a drain of which is connected to the other end
of the organic light emitting diode.
19. The driving method of an AMOLED panel according to claim 17,
wherein the driving circuit further includes a fourth transistor, a
gate of which is connected to the row scan signal terminal, a
source of which is connected to one end of the organic light
emitting diode and a drain of which is connected to the other end
of the organic light emitting diode.
20. The driving method of an AMOLED panel according to claim 18,
wherein the driving transistor and the first to fourth transistors
are N-type transistors.
Description
BACKGROUND
[0001] One or more embodiments of the present disclosure relate to
an active matrix organic light emitting diode (AMOLED) panel, a
driving circuit and driving method for the AMOLED panel.
[0002] As compared with conventional thin film transistor liquid
crystal display (TFT-LCD) panels, AMOLED panels have advantages
such as faster response speed, higher contrast, wider view angles,
and so on, and thus are regarded as the next generation of display
technology, drawing much attention from most of the developers in
display technology.
[0003] A sub-pixel unit of an AMOLED panel emits light is driven by
a driving circuit. A conventional 2T1C driving circuit for each
sub-pixel unit comprises two transistors (2T) and one capacitor
(1C), as illustrated in FIG. 1. In FIG. 1, a transistor M1 acts as
a switching transistor, a transistor M2 acts as a driving
transistor, and a capacitor C acts as a storage capacitor. The
transistor M1 is controlled by a row scan line signal Vscan so as
to control the input of a data voltage Vdata. The transistor M2 is
used for controlling an organic light emitting diode (OLED) to emit
light. The storage capacitor C is used for providing a maintaining
voltage to the gate of the transistor M2.
[0004] FIG. 2 is a control timing chart of the conventional 2T1C
driving circuit in FIG. 1. The operation procedure of the 2T1C
driving circuit is as follows. Two stages T1, T2 in FIG. 2 are
taken for example, wherein the stage T1 is a writing stage of the
display data voltage and the stage T2 is a display maintaining
stage. During the stage T1, the row scan line signal Vscan is at a
high level, and the transistor M1 is turned on, thus the data
voltage Vdata charges the storage capacitor C and the data voltage
Vdata is transferred to the gate of the transistor M2 at the same
time, such that the transistor M2 works in a saturation status, and
the organic light emitting diode (OLED) is driven to emit light.
During the stage T2, the row scan line signal Vscan is changed to a
low level, and the transistor M1 is turned off, so the data voltage
Vdata cannot reach the gate of the transistor M2 and the storage
capacitor C provides the gate of the transistor M2 with the
maintaining voltage, such that the transistor M2 continues to work
in the saturation status, which makes the OLED emit light
continuously. Thereafter, the 2T1C driving circuit repeats the
stage T2 until next stage T1 arrives.
[0005] It can be known from the above that the OLED in each pixel
of the AMOLED panel is capable of emitting light with a driving
current generated when the driving transistor M2 works in the
saturation status. In particular, the driving current (i.e., the
current flowing through the OLED) I=K(V.sub.gs-V.sub.th).sup.2,
wherein V.sub.g, is a voltage difference between the gate and
source of the transistor M2, V.sub.th is a threshold voltage of the
transistor M2, and K is a constant related to the structure and the
manufacturing process of the transistor M2 per se. At present, the
threshold voltages V.sub.1, of transistors have bad uniformity in
the low temperature poly-silicon process, and may shift in usage,
thus different threshold voltages of the transistor M2 result in
different driving currents over time even if a same data voltage
Vdata is input to the gate of the transistor M2, which makes worse
brightness uniformity for the AMOLED panel.
SUMMARY
[0006] One or more embodiments of the present disclosure provide an
active matrix organic light emitting diode (AMOLED) panel and a
driving circuit and a driving method for the panel so as to improve
the brightness uniformity of the AMOLED panel.
[0007] According to an aspect of the disclosure, a driving circuit
of an active matrix organic light emitting diode panel comprising,
a driving transistor, a first transistor, a second capacitor, an
organic light emitting diode, and a voltage adjustment module,
wherein the driving transistor comprises a gate which is connected
to the second capacitor, a source which is connected to a low level
signal terminal, and a drain which is connected to the voltage
adjustment module; the first transistor comprises a gate which is
connected to a row scan signal terminal, a source which is
connected to the voltage adjustment module, and a drain which is
connected to a data signal terminal; the second capacitor is
connected between the gate of the driving transistor and the low
level signal terminal; the organic light emitting diode is
connected between the low level signal terminal and a juncture of
the source of the driving transistor with the second capacitor, or
is connected between a high level signal terminal and the drain of
the driving transistor; and the voltage adjustment module is
connected to a first control signal terminal, a second control
signal terminal and the high level signal terminal, and further is
connected with the second capacitor, the gate of the driving
transistor, and the source of the first transistor, for adjusting a
gate-source voltage of the driving transistor connected with the
second capacitor, such that a driving current of the driving
transistor in a saturation status is independent of the threshold
voltage of the driving transistor.
[0008] According to another aspect of the disclosure, an active
matrix organic light emitting diode panel comprises a plurality of
sub-pixel units arranged in matrix, and one driving circuit as
mentioned above is provided to each of the sub-pixel units.
[0009] According to further another aspect of the disclosure, a
driving method for an active matrix organic light emitting diode
(AMOLED) panel comprising driving the AMOLED panel with the driving
circuit as described above for each sub-pixel units of the AMOLED
panel, such that a driving current of the driving transistor under
a saturation status in the driving circuit is independent of the
threshold voltage of the driving transistor.
[0010] In the active matrix organic light emitting diode panel and
the driving method and the driving circuit therefor in one or more
embodiments of the present disclosure, the driving current of the
driving transistor in the driving circuit in the saturation status
can be independent of its threshold voltage, thus the threshold
voltage V.sub.th will not affect the current flowing through an
organic light emitting diode, so that the consistency (or
uniformity) of the driving circuit can be ensured in a better way,
which renders good AMOLED brightness uniformity.
[0011] Further scope of applicability of the present disclosure
will become apparent from the detailed description given
hereinafter. However, it should be understood that the detailed
description and specific examples, while indicating preferred
embodiments of the disclosure, are given by way of illustration
only, since various changes and modifications within the spirit and
scope of the disclosure will become apparent to those skilled in
the art from the following detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The present disclosure will become more fully understood
from the detailed description given hereinafter and the
accompanying drawings which are given by way of illustration only,
and thus are not limitative of the present disclosure and
wherein:
[0013] FIG. 1 is a schematic diagram of a conventional 2T1C driving
circuit;
[0014] FIG. 2 is a control timing chart of the 2T1C driving circuit
illustrated in FIG. 1;
[0015] FIG. 3 is a schematic diagram of an AMOLED driving circuit
according to an embodiment of the present disclosure;
[0016] FIG. 4 is a schematic diagram of one embodiment of an AMOLED
driving circuit;
[0017] FIG. 5 is a control timing chart of the AMOLED driving
circuit illustrated in FIG. 4;
[0018] FIG. 6 is a schematic diagram of operation of the AMOLED
driving circuit illustrated in FIG. 4 in stage t1;
[0019] FIG. 7 is a schematic diagram of operation of the AMOLED
driving circuit illustrated in FIG. 4 in stage t2;
[0020] FIG. 8 is a schematic diagram of operation of the AMOLED
driving circuit illustrated in FIG. 4 in stage t3;
[0021] FIG. 9 is a schematic diagram of operation of the AMOLED
driving circuit illustrated in FIG. 4 in stage t4; and
[0022] FIG. 10 is a schematic diagram of another embodiment of the
AMOLED driving circuit.
DETAILED DESCRIPTION
[0023] The active matrix organic light emitting diode (hereinafter
called as AMOLED) and the driving method and circuit thereof
according to the embodiments of the present disclosure will be
described below in details with reference to the accompanying
figures. The description is made only for the purpose of
illustration but not in a limitative way.
[0024] FIG. 3 is a schematic diagram of an AMOLED driving circuit
according to an embodiment of the present disclosure. The driving
circuit according to the present embodiment is for example used in
a sub-pixel of an AMOLED panel and includes two transistors, one
capacitor, one organic light emitting diode (OLED), one voltage
adjustment module, and input and output terminals. The AMOLED
comprises multiple sub-pixels arranged in matrix for example. In
each AMOLED driving circuit, the respective input and output
terminals include a row scan signal terminal Scan, a data signal
terminal Vdata, a first control signal terminal CR1, a second
control signal terminal CR2, a high level signal terminal Vdd, and
a low level signal terminal Vss. In particular, the AMOLED driving
circuit includes the following components and configuration.
[0025] A driving transistor DTFT comprises a gate connected to a
second capacitor C2, a source connected to the low level signal
terminal Vss, and a drain connected to a voltage adjustment module
1; the driving transistor DTFT acts as a driving transistor for
providing a driving current when it works in a saturation status to
drive the OLED to emit light. A first transistor T1 comprises a
gate connected to the row scan signal terminal Scan, a source
connected to the voltage adjustment module 1, and a drain connected
to the data signal terminal Vdata; the transistor T1 is used as a
switching transistor for controlling the input of the data signal
terminal Vdata under the control of the row scan signal terminal
Scan. A second capacitor C2 is connected between the gate of the
driving transistor DTFT and the low level signal terminal Vss, and
is used for providing a maintaining voltage to the gate of the
driving transistor DTFT. An organic light emitting diode (OLED) is
connected between the low level signal terminal Vss and a juncture
of the source of the driving transistor DTFT with the second
capacitor C2 (see FIGS. 3 and 4), i.e., the source of the driving
transistor DTFT is connected to the second capacitor C2 and then
connected to the organic light emitting diode (OLED); or in another
example, the OLED is connected between a high level signal terminal
Vdd and the drain of the driving transistor DTFT (see FIG. 10). The
OLED can emit light under the action of the driving current of the
driving transistor DTFT whereby the whole AMOLED panel can operate
to display. The voltage adjustment module 1 is connected to the
first control signal terminal CR1, the second control signal
terminal CR2 and the high level signal terminal Vdd, and further is
connected with the second capacitor C2, the gate of the driving
transistor DTFT and the source of the first transistor T1; and this
voltage adjustment module 1 is used for adjusting the gate-source
voltage V.sub.gs of the driving transistor DTFT connected with the
second capacitor C2, such that the driving current I of the driving
transistor DTFT in a saturation status is independent of the
threshold voltage V.sub.th of the driving transistor DTFT.
[0026] In the embodiments of the AMOLED driving circuit of the
present disclosure, since the gate-source voltage V.sub.gs of the
driving transistor DTFT connected with the second capacitor C2 can
be adjusted by the voltage adjustment module 1 so as to render the
driving current I of the driving transistor DTFT in the saturation
status independent of the threshold voltage V.sub.th of DTFT, the
threshold voltage V.sub.th of the driving transistor DTFT will not
affect the current flowing through the OLED, thus a consistency of
the driving circuit I can be maintained in a better way, which
gives rise to the better brightness uniformity of the AMOLED
panel.
[0027] FIG. 4 is a schematic diagram of one specific embodiment of
an AMOLED driving circuit. As known from FIG. 4, the AMOLED driving
circuit includes five transistors, two storage capacitors, one
light emitting element, and input and output terminals. In FIG. 4,
the five transistors include a driving transistor DTFT, a first
transistor T1, a second transistor T2, a third transistor T3, and a
fourth transistor T4 respectively. The storage capacitors include a
first capacitor C1 and a second capacitor C2. The light emitting
element is an organic light emitting diode (OLED). The input and
output terminals include a row scan signal terminal Scan, a data
signal terminal Vdata, a first control signal terminal CR1, a
second control signal terminal CR2, a high level signal terminal
Vdd, and a low level signal terminal Vss.
[0028] The configuration of the AMOLED driving circuit in the
present embodiment is as the following. The driving transistor DTFT
comprises a gate connected to the second capacitor C2, a source
connected to the low level signal terminal Vss and a drain
connected to the source of the third transistor T3. The first
transistor T1 comprises a gate connected to the row scan signal
terminal Scan, a source connected to the first capacitor C1, a
drain connected to the data signal terminal Vdata. The second
transistor T2 comprises a gate connected to the first control
signal terminal CR1, a source connected to the second capacitor C2
(and is connected with the first capacitor C1 and the gate of the
driving transistor DTFT at the same time), a drain connected to the
drain of the driving transistor DTFT (and is connected with a
source of third transistor T3 at the same time). The third
transistor T3 comprises a gate connected to the second control
signal terminal CR2, a source connected to the drain of the driving
transistor DTFT (and is connected with the drain of the second
transistor T2 at the same time), and a drain connected to the high
level signal terminal Vdd. The fourth transistor T4 comprises a
gate connected to the row scan signal terminal Scan, a source
connected to one end of the organic light emitting diode (OLED) and
the low level signal terminal Vss, and a drain connected to the
other end of the OLED and the source of the transistor DTFT. The
first capacitor C1 is connected between the source of the first
transistor T1 and the second capacitor C2 (and at the same time the
end adjacent to the second capacitor C2 is also connected with the
gate of the driving transistor DTFT and the source of the second
transistor T2). The second capacitor C2 is connected between the
gate of the driving transistor DTFT and the source of the driving
transistor DTFT (and the end adjacent to the gate of the transistor
DTFT is also connected to the first capacitor C1 and the source of
the second transistor T2, and the other end adjacent to the source
of the transistor DTFT is also connected to the drain of the fourth
transistor T4). The OLED is connected between the low level signal
terminal Vss and a juncture of the source of the driving transistor
DTFT with the second capacitor C2. In particular, the source of the
driving transistor DTFT is connected with the second capacitor C2
and then with the OLED, as illustrated in FIG. 4.
[0029] In FIG. 4, the second transistor T2, the third transistor T3
and the first capacitor C1 together constitute the voltage
adjustment module 1 in the present embodiment. The voltage
adjustment module 1 adjusts the gate-source voltage V.sub.gs of the
driving transistor DTFT connected with the second capacitor C2,
such that the driving current I of the driving transistor DTFT in
the saturation status can be independent of the threshold voltage
V.sub.th of the driving transistor DTFT. Therefore, although
I=K(V.sub.gs-V.sub.th).sup.2, the threshold voltage V.sub.th of the
driving transistor DTFT will not affect the current flowing through
the OLED when the OLED is emitting light by addition of the voltage
adjustment module, so that the consistency of the driving circuit I
can be ensured in a better way, which brings about good AMOLED
brightness uniformity.
[0030] The source and drain of the fourth transistor T4 are
connected to the two ends of the OLED, respectively, and therefore
the OLED is shorted when the driving transistor DTFT generates an
incorrect driving current to prevent the OLED from emitting light
under the action of the incorrect driving current and generating
incorrect luminous strength, which may result in abnormal display.
Further, the OLED is in connectivity with the driving transistor
DTFT when the driving transistor DTFT generates a correct driving
current, so that the OLED emits light under the action of the
correct driving current, which ensures normal display.
[0031] A first node A is set between the first capacitor C1 and the
second capacitor C2, and also is connected with the gate of the
driving transistor DTFT and the source of the second transistor T2.
A second node B is set between the source of the driving transistor
DTFT and the OLED, and is also connected with the second capacitor
C2 and the drain of the fourth transistor T4. A third node C is set
between the first capacitor C1 and the source of the first
transistor T1. The first node A, the second node B and the third
node C can facilitate to describe and calculate circuit parameters
(such as voltages at respective nodes) of the AMOLED driving
circuit in the following.
[0032] For example, all of the driving transistor DTFT, the first
transistor T1, the second transistor T2, the third transistor T3
and the fourth transistor T4 may be N-type transistors, which can
be turned on under a high level signal and turned off under a low
level signal.
[0033] In terms of functions of the transistors in the AMOLED
driving circuit, the first transistor T1, the second transistor T2,
the third transistor T3 and the fourth transistor T4 are switching
transistors for turning on or off circuit connections. Thus, in the
AMOLED driving circuit illustrated in FIGS. 6-9, the first to
fourth transistors T1-T4 are simplified, i.e., the transistors that
are turned off are omitted (not shown in the FIGS. 6-9), and the
transistors that are turned on are simplified as conductive lines.
The driving transistor DTFT is a driving transistor for generating
the driving current to drive the OLED to emit light when this
transistor is operating in the saturation status. It should be
noted that the driving transistor DTFT and the first to fourth
transistors T1-T4 are substantially the same in fabrication
processes and structures, and they are named differently here only
for distinguishing their functions in the AMOLED driving
circuit.
[0034] FIG. 5 is a control timing chart of the AMOLED driving
circuit in the present embodiment, and four stages t1 to t4 are
selected for example. In the following descriptions, the high level
signal is represented with digit "1," and the low level signal is
represented with digit "0." The operation of the AMOLED driving
circuit is described as follows with reference to FIGS. 5 and
6-9.
[0035] During the stage t1, Scan=1, V.sub.data V.sub.L, CR1=1, and
CR2=1.
[0036] The stage t1 is a pre-charge stage. As illustrated in FIG.
6, during the stage t1, since the row scan signal terminal Scan is
at the high level, both of the first transistor T1 and the fourth
transistor T4 are turned on; since the first control signal
terminal CR1 is at the high level, the second transistor T2 is
turned on; since the second control signal terminal CR2 is at the
high level, the third transistor T3 is turned on. At this time, the
low level data "V.sub.L" is input from the data signal terminal
Vdata to the first capacitor C1 via the first transistor T1; the
high level signal from the high level signal terminal Vdd reaches
the first node A via the third transistor T3 and the second
transistor T2, and the driving transistor DTFT is turned on due to
this high level signal. At this time, the gate and drain of the
driving transistor DTFT are connected through the second transistor
T2, thus the gate voltage and the drain voltage of the driving
transistor DTFT are identical to each other, i.e., the gate-source
voltage V.sub.gs equals to the drain-source voltage V.sub.ds of the
driving transistor DTFT, which can satisfy
V.sub.ds.gtoreq.V.sub.gs-V.sub.th. Therefore, the driving
transistor DTFT operates in the saturation status, the driving
transistor DTFT in the saturation status generates a driving
current of
I=K(V.sub.gs-V.sub.th).sup.2=K(V.sub.qn-V.sub.th).sup.2=K(Vdd-V.sub.th).s-
up.2, where V.sub.gs is the voltage difference between the gate and
the source of the driving transistor DTFT, V.sub.th is the
threshold voltage of the driving transistor DTFT, and K is a
constant related to the driving transistor DTFT per se. In
addition, the source of the driving transistor DTFT is connected to
the low level signal terminal Vss via the fourth transistor T4.
Meanwhile, the voltage V.sub.a at the first node A is equal to Vdd
(V.sub.a=Vdd); the voltage V.sub.b at the second node B is equal to
Vss (V.sub.b=Vss); and the voltage V.sub.c at the third node C is
equal to V.sub.data (data voltage) and therefore V.sub.L
(V.sub.c=V.sub.data-V.sub.L). Since the driving circuit I at this
time is not the correct driving circuit I which is preset for the
OLED, the fourth transistor T4 is turned on during the stage t1 for
making the OLED shorted and preventing the OLED from emitting
light, in order to prevent the OLED from generating light at an
incorrect luminance strength.
[0037] During the stage t2, Scan=1, V.sub.data=V.sub.L, CR1=1, and
CR2=0.
[0038] The stage t2 is a discharging stage. As illustrated in FIG.
7, during the stage t2, since the row scan signal terminal Scan is
at the high level, the first transistor T1 and the fourth
transistor T4 continue to be turned on; since the first control
signal terminal CR1 is at the high level, the second transistor T2
continue to be turned on; since the second control signal terminal
CR2 is at the low level, the third transistor T3 is turned off. At
this time, since the second transistor T2 is turned on but the
third transistor T3 is turned off, the gate and the source of the
driving transistor DTFT are connected together, and the drain of
the transistor DTFT is disconnected from the third transistor T3,
in which case the driving transistor DTFT works as a diode, and the
first capacitor C1, the driving transistor DTFT and the low level
signal terminal Vss together form a discharging loop (as shown by
the arrow in FIG. 7) for discharging the first capacitor C1. This
discharging procedure goes on until the voltage at the first node A
falls to the threshold voltage V.sub.th of the driving transistor
DTFT, and at this time, the driving transistor DTFT is at a
critical turning-on status, and if the discharging continues, the
driving transistor DTFT will be turned off, thus the discharging
loop will disconnects and the discharging procedure ends. At this
time, a voltage V.sub.c1 between the two terminals of the first
capacitor C1 is equal to V.sub.c-V.sub.a=V.sub.L-V.sub.th
(V.sub.c1=V.sub.c-V.sub.a-V.sub.L-V.sub.th). The voltage V.sub.a at
the first node A is equal to Vdd (V.sub.a=Vdd); the voltage V.sub.b
at the second node B is equal to Vss (V.sub.b=Vss); and the voltage
V.sub.c at the third node C is equal to V.sub.data
(V.sub.c=V.sub.data=V.sub.L). The fourth transistor T4 is turned on
during the stage t2 for making the OLED shorted, so that the OLED
is prevented from emitting light.
[0039] During the stage t3, Scan=1, Vdata=V.sub.H, CR1=0, and
CR2=0.
[0040] The stage t3 is a voltage adjustment stage. As illustrated
in FIG. 8, during the stage t3, since the row scan signal terminal
Scan is at the high level, the first transistor T1 and the fourth
transistor T4 continued to be turned on; since the first control
signal terminal CR1 is at the low level, the second transistor T2
is turned off; since the CR2 is at the low level, the third
transistor T3 is turned off. At this time, since the first
transistor T1 is turned on, the data signal terminal Vdata is
connected to the first capacitor C1 via the third node C, and since
the Vdata becomes the high voltage V.sub.H from the low voltage
V.sub.L sharply, the voltage at the third node C sharply changes to
V.sub.H from V.sub.L correspondingly. Since both the second
transistor T2 and the third transistor T3 are turned off, and the
driving transistor DTFT is at the critical status and is not turned
on, the first node A is in a floating status. When the voltage at
the third node C changes sharply, the first capacitor C1 in the
floating status can keep unchanged the charges at its respective
ends, and thus the charges at the first node A remain unchanged
also, and therefore the voltage at the first node A changes sharply
accordingly. During the stage t3, the charges at the first node A
can be expressed by a formula
Q.sub.a=(V.sub.a-V.sub.c).times.C.sub.2+(V.sub.a-Vss).times.C.sub.2,
where Q.sub.a represents the charges at the first node A, C.sub.1
represents capacitance of the first capacitor C1, and C.sub.2
represents capacitance of the second capacitor C2. Hereby, it can
be known that the charges of the first node A before the sharp
change of the voltage satisfy
(V.sub.th-V.sub.L).times.C.sub.1+(V.sub.th-Vss).times.C.sub.2, and
the charges of the first node A after the sharp change of the
voltage satisfy
(V.sub.a-V.sub.H).times.C.sub.1+(V.sub.a-Vss).times.C.sub.2. These
results are equal to each other, i.e.,
(V.sub.th-V.sub.L).times.C.sub.1+(V.sub.th-Vss).times.C.sub.2=(V.sub.a-V.-
sub.H).times.C.sub.1+(V.sub.a-Vss).times.C.sub.2. It can be known
that the voltage at the first node A changes to
V.sub.a=V.sub.th+(V.sub.H-V.sub.L).times.C.sub.1/(C.sub.1+C.sub.2)
sharply. Meanwhile, as for the voltage V.sub.a at the first node A,
V.sub.a=V.sub.th+(V.sub.H-V.sub.L).times.C.sub.1/(C.sub.1+C.sub.2);
as for the voltage V.sub.b at the second node B, V.sub.b=Vss; and
as for the voltage V.sub.c at the third node C,
V.sub.c-V.sub.data(data voltage)=V.sub.H.
[0041] During the stage t4, Scan=0, Vdata=V.sub.L, CR1=0, and
CR2=1.
[0042] The stage t4 is a driving stage. As illustrated in FIG. 9,
during the stage t4, since the row scan signal terminal Scan is at
the low level, the first transistor T1 and the fourth transistor T4
are turned off; since the first control signal terminal CR1 is at
the low level, the second transistor T2 is turned off; since the
second control signal terminal CR2 is at the high level, the third
transistor T3 is turned on. At this time, since the voltage at the
first node A rises to
V.sub.th+(V.sub.H-V.sub.L).times.C.sub.1/(C.sub.1+C.sub.2), the
driving transistor DTFT is turned on and operates in the saturation
status. At this time, the third transistor T3 is turned on also,
and therefore the high level signal terminal Vdd, the third
transistor T3, the driving transistor DTFT, the organic light
emitting diode (OLED) and the low level signal terminal Vss
together form a driving loop, and the driving current in the
driving loop satisfy:
I = K ( V gs - V th ) 2 = K ( V ab - V th ) 2 = K ( V th + ( V H -
V L ) .times. C 1 / ( C 1 + C 2 ) - V th ) 2 = K ( ( V H - V L )
.times. C 1 / ( C 1 + C 2 ) ) 2 . ##EQU00001##
[0043] It can be known that the driving current generated by the
driving transistor DTFT in the saturation status is independent of
its threshold voltage V.sub.th, and thus the OLED can emit light
with the stable driving current, so that the consistency of the
driving circuit I can be ensured in a better way.
[0044] Thereafter, the AMOLED driving circuit repeats the stage t4
until the next stage t1 arrives. It can be known from the above
descriptions that the driving current I for driving OLED to emit
light is independent of the threshold voltage V.sub.th of the
driving transistor DTFT during the stage t4, thus the threshold
voltage V.sub.th, will not affect the current flowing through the
organic light emitting diode OLED, so that the consistency of the
driving circuit can be ensured better, which brings about better
uniformity of AMOLED brightness.
[0045] In addition, FIG. 10 is an AMOLED driving circuit in another
embodiment. The AMOLED driving circuit in this embodiment is
basically the same as the AMOLED driving circuit in the embodiment
illustrated in FIG. 4 except the connection position of the OLED.
In the present embodiment, the OLED is connected between the high
level signal terminal Vdd and the drain of the driving transistor
DTFT. Specifically as shown in FIG. 10, the OLED is connected
between the high level signal terminal Vdd and the drain of the
third transistor T3. As for the AMOLED driving circuit illustrated
in FIG. 10, the control timing chart thereof is the same as that
shown in FIG. 5, and the operation procedure thereof is the same as
that described above, thus detailed description is omitted here for
simplicity. It needs to be noted that the difference in structure
between the embodiment shown in FIG. 4 and that shown in FIG. 5
leads to some tiny difference of the final result. In the
embodiment as shown in FIG. 10, since the OLED is connected between
the source of the first transistor T4 and the low level signal
terminal Vss, a voltage V.sub.oled.sub.--.sub.in will be generated
across the two ends of the OLED in operation, that is, the
V.sub.oled.sub.--.sub.in is the voltage across the OLED when it is
emitting light. At this time, due to this voltage across the OLED,
V.sub.q=Vss+V.sub.th+(V.sub.ref-V.sub.data);
V.sub.n=Vss+V.sub.oled.sub.--.sub.in; and
V.sub.gs=V.sub.qn=(V.sub.ref-V.sub.data)+V.sub.th-V.sub.oled.sub.--.sub.i-
n. Therefore,
I=k(V.sub.ref-V.sub.data-V.sub.oled.sub.--.sub.in).sup.2 finally.
In this way, the voltage V.sub.oled.sub.--.sub.in is introduced to
the final result of the driving circuit I. The voltage
V.sub.oled.sub.--.sub.in differs slightly when V.sub.data is at
different gray level voltages, which brings forth somewhat
instability during the circuit works. Therefore, the embodiment
illustrated in FIG. 10 is different as compared with that
illustrated in FIG. 4.
[0046] It should be understood that the technical schemes of the
embodiments illustrated above in FIGS. 4 and 10 are not only
suitable for polysilicon transistors but also suitable for other
kinds of transistors in practice.
[0047] Moreover, another embodiment of the present disclosure also
provides an active matrix organic light emitting diode (AMOLED)
panel which comprises a plurality of sub-pixel units arranged in
matrix, and one driving circuit as described above is provided in
each of the sub-pixel units correspondingly. The driving circuit
can be that as shown in FIG. 3, and for example, the AMOLED driving
circuit shown in FIG. 4 or the AMOLED driving circuit shown in FIG.
10. The sub-pixel units of the AMOLED panel may comprise OLEDs for
emitting red, green, and blue light respectively and therefore
constitute red, green, and blue sub-pixel units. When the sub-pixel
units emit light under control in a conventional way for example,
colorful display can be realized.
[0048] With reference to FIG. 3, the AMOLED driving circuit in the
AMOLED panel of the embodiment of the present disclosure includes
two transistors, a capacitor, a organic light emitting diode, a
voltage adjustment module, and input and output terminals. As for
each AMOLED driving circuit, the input and output terminals include
a row scan signal teiminal Scan, a data signal terminal Vdata, a
first control signal terminal CR1, a second control signal terminal
CR2, a high level signal terminal Vdd and a low level signal
terminal Vss. In particular, the AMOLED driving circuit includes
the following components and configuration.
[0049] A driving transistor DTFT comprises a gate connected to a
second capacitor C2, a source connected to the low level signal
terminal Vss, and a drain connected to the voltage adjustment
module 1; the transistor DTFT acts as a driving transistor for
providing a driving current to drive the OLED to emit light when
the driving transistor DTFT works in a saturation status. A first
transistor T1 comprises a gate connected to the row scan signal
terminal Scan, a source connected to the voltage adjustment module
1, and a drain connected to the data signal terminal Vdata; the
first transistor T1 acts as a switching transistor for controlling
the input of the data signal terminal Vdata under the control of
the row scan signal terminal Scan. A second capacitor C2 is
connected between the gate of the driving transistor DTFT and the
low level signal terminal Vss, and is used for providing a
maintaining voltage to the gate of the driving transistor DTFT. The
organic light emitting diode (OLED) is connected between the low
level signal terminal Vss and a juncture of the source of the
driving transistor DTFT with the second capacitor C2 (see the FIGS.
3 and 4), i.e., the source of the driving transistor DTFT is
connected to the second capacitor C2 and then connected to the
OLED; or in another example, the OLED is connected between the high
level signal terminal Vdd and the drain of the driving transistor
DTFT (see the FIG. 10). The OLED emits light under the action of
the driving current of the driving transistor DTFT whereby the
whole AMOLED panel can operate to display. The voltage adjustment
module 1 is connected to the first control signal terminal CR1, the
second control signal terminal CR2 and the high level signal
terminal Vdd, and further is connected with the second capacitor
C2, the driving transistor DTFT and the first transistor T1; and
this voltage adjustment module 1 is used for adjusting a
gate-source voltage V.sub.gs of the driving transistor DTFT
connected with the second capacitor C2, such that the driving
current I of the driving transistor DTFT in a saturation status is
independent of the threshold voltage V.sub.th of the driving
transistor DTFT.
[0050] In the AMOLED driving circuit provided by the embodiment of
the present disclosure, since the gate-source voltage V.sub.gs of
the driving transistor DTFT connected with the second capacitor C2
can be adjusted by the voltage adjustment module 1, the driving
current I of the driving transistor DTFT in the saturation status
is independent of its threshold voltage V.sub.th, and the threshold
voltage V.sub.th of the driving transistor DTFT will not affect the
current flowing through the OLED, so that the consistency of the
driving circuit I can be ensured in a better way, which renders
good uniformity of AMOLED brightness.
[0051] Moreover, further another embodiment of the present
disclosure also provides an AMOLED driving method. In this
embodiment, the sub-pixel units of the AMOLED panel are driven with
the above-described AMOLED driving circuits, such that in each of
the driving circuit, the driving current of a driving transistor in
the saturation status is independent of the threshold voltage of
the driving transistor. The driving circuits of the AMOLED panel
can include the driving circuits as shown in FIG. 3, FIG. 4, or
FIG. 10 above, but this is not limitative, and the panel can
further include other kinds of driving circuits.
[0052] In the AMOLED driving method provided by the embodiment of
the present disclosure, the driving current of the driving
transistor in the saturation status in the AMOLED driving circuit
can be independent of its threshold voltage, thus the threshold
voltage V.sub.th will not affect the current flowing through the
OLED of the respective sub-pixel unit, so that the consistency of
the driving circuit can be ensured better, which renders good
uniformity of AMOLED brightness.
[0053] In the present embodiment, in order that the driving current
of the driving transistor in the saturation status in the driving
circuit is independent of its threshold voltage, a voltage
adjustment module can be added to the driving circuit; this voltage
adjustment module is adapted to adjust a gate-source voltage of the
driving transistor, such that the driving current of the driving
transistor in the saturation status is independent of its threshold
voltage. The driving transistor means a transistor for providing a
driving current to the respective OLED, and the threshold voltage
means the threshold voltage of the driving transistor. The
gate-source voltage V.sub.gs refers to a voltage difference between
the gate voltage V.sub.g and the source voltage V.sub.s of the
driving transistor. V.sub.th can be included as a component of
V.sub.gs by adjusting V.sub.gs with the voltage adjustment module,
such that the V.sub.th can be counteracted or offset because
I=K(V.sub.gs-V.sub.th).sup.2 and the driving circuit I is
independent of the threshold voltage V.sub.th finally.
[0054] In order that the driving transistor in the driving circuit
operates in the saturation status, the driving circuit can be
constructed such that the difference value between the gate-source
voltage of the driving transistor and the threshold voltage thereof
is less than or equals to a source-drain voltage of the driving
transistor, i.e., satisfying V.sub.ds.gtoreq.V.sub.gs-V.sub.th.
When the driving transistor operates in the saturation status, the
driving circuit I of the driving transistor only depends on its
gate-source voltage V.sub.gs. At this time, the voltage adjustment
module can only adjust the gate-source voltage V.sub.gs, and
therefore parameters to be adjusted are in a small number and thus
the adjustment procedure is simple.
[0055] Several embodiments of an AMOLED panel and an AMOLED driving
circuit and method therefor are provided in the above.
[0056] The above descriptions only present some embodiments of the
present disclosure, and the protection scope of the present
disclosure is not limited to these embodiments. Those skilled in
the art can easily conceive modifications or alternations within
the technical scope of the present disclosure. Therefore, the
protection scope of the present disclosure should be defined by the
following claims.
* * * * *